Life in the clouds: songbird pattern in the Western Ghats

Across the world, mountains harbour high biodiversity. This is thought to be because of the array of habitats that exist along the mountain slope. But could the structure of mountain range, its ups and downs contribute to driving biodiversity? It was these questions that the group led by Uma Ramakrishnan set out to answer. Focussing on the Western Ghats, a global biodiversity hotspot and home to high elevation songbirds, a paper published today in the Proceedings of Royal Society B has found that birds living in high elevation peaks of the Western Ghats of southern India are affected by gaps in forest cover to different extents; deep valleys have greater impact than shallow ones along a mountain chain.

At 1400 metres above sea level, the Sky Islands or Sholas are a habitat home to a genetically diverse community of songbirds, with as many as 23 species sharing the same habitat. The mountains are interrupted by deep valleys that fragment the habitat of these birds. The 40 km long Palghat Gap is the largest and oldest gap in the Western Ghats, followed by the Shenkottah Gap and the Chaliyar River valley. "I have studied high elevation songbirds in the Western Ghats for the last fifteen years, and always wondered how the mountain itself effected differences between populations. Do valleys in the mountain range function as barriers for these mountain-top species? Do all species respond similarly to these valleys? Has changing climate played a role? asks VV Robin, the corresponding author of the study.

The group sampled birds from populations across the mountain range, generated genetic data for these individuals and then used phylogenetic analyses to test the effects of these valleys on different species. If a valley is a barrier, populations on either side are genetically more different and begin to diverge, potentially into new species. The study found that not all species are affected by the gaps. Out of the 23 species studied, 10 showed genetic divergences across the deepest, widest valley, the Palghat gap, while three of these diverged across the Shenkotta gap. Only one species diverged across the shallowest valley, the Chaliyar River valley.

"It was a thrilling experience to stay and explore many of the mountain tops in the Ghats as part of this unique research project." said CK Vishnudas, a co-author of the paper who did much of the field work. Spending close to 400 nights out in the field, the researchers were able to collect genetic data from 356 individuals across three years. "Our study shows that it was not just the mountain valleys, but the climate that moves the habitat up and down the mountain and had an important role in these bird divergences. So, going by their response to historic climate change, we can predict that future climate change may impact these birds" said Robin.

The study also highlights the importance of sampling a large number of species, rather than just one or two from a community. "Many studies have focused on a few species; however, studying an entire community provides a common framework to analyze the effects of topology across species", says Ramakrishnan. "Our results reveal richly varied, yet generalizable patterns. The nested patterns of divergence across deeper versus shallower valleys also provide clear predictions. We now know where to look for the two most different individuals in a species: they should be across the Palghat gap!"

The exhilaration that follows on the heels of such a mammoth effort is neatly summed up by Pooja Gupta, another co-author, who said "It was an amazing experience going from the birds in the mountains to the large amount of genetic data we generated in the lab." Such studies promise to reveal more about how diversity is generated in the natural world.

About the paper:

The paper can be accessed at Proceedings of the Royal Society. This work was supported by a National Geographic Society Research and Exploration grant to V.V.Robin, a DAE award to study Indian Biogeography, Ramanujan Fellowship and NCBS intramural funding to Uma Ramakrishnan.

Comments

This is just a an exquisite display of the western ghats. The pictures are beautiful and perfectly timed. Just the other day i was planning a hiking trip to the western ghats in maharashtra after reading a certain article ( I am also posting a link so that everyone can get the idea) but I was highly indecisive. After reading this article i feel i should take a trip to the whole of western ghats !!!! :-D